MODIFIED LATEX

Abstract: A method is disclosed for the use of a modified latex making it possible to provide a combination of hydrogene bonds and covalent bonds in fibrous products. A softener product is added to the binder solution before its application onto the fibrous product. The softener is a natural latex added to a latex binder contained in a water suspension. It has surprisingly shown that a product manufactured with a modified latex will occur more soft and silky and also stronger than products made by use of a normal latex binder. The modified latex is especially suitable for use in a process in which a mechanical softening treatment is effected on the fibrous product.

Description: MODIFIED LATEX This invention concerns a method for production of a binder solution making it possible to produce a softer and stronger air-laid product having groups of fibers bonded to other fibers and other groups of fibers. The soft and silky effect is obtained through a modification of the binder making it possible to reduce the amount of binder and easy to effect a neutralizing or at least a partly neutralizing of the brittle bonds which normally is provided in the form of cellulosic hydrogen bonds and/or casein bonds. It is a neccessity to apply SBR latex binders or other binders in an aqueous suspension onto a dry laid product of fibrous material in order to form an effective bond between individual fibers and groups of fibers. After the air-laying of the fibers onto a forming surface the binder solution or suspension is applied onto the fibrous product. After the applying of such solution or suspension in one or several application stations the web is normally led through a drying unit and then through a curing unit leaving the hydrogen bond untouched in the dry formed paper. When applying the binder solution a combination of brittle hydrogen bonds and elastic bonds are necessarily provided together. The hydrogen bonds are valuable in a fibrous product although they are generally an irritation to the human skin. However, the hydrogen bonds are not brittle when they only stay in small groups of few fiber- agglomerations or between single fibers. These hydrogen bonds make the overall product stronger. However, due to the brittleness of the hydrogen bonds the fibrous product would appear as a rather stiff web having a poor hand and feel. Also the drapability would be poorer than wanted. The elastic latex bonds are valuable. However, since the latex is applied in a suspension of water, therefore accordingly, a hydrogen bond would also be provided together with a latex bond. It is an object of the present invention to provide a binder solution which makes it possible to manufacture a softer and more silky air-laid fibrous product in which the fibers and groups of fibers are bonded together with other fibers or groups of fibers via a combination of hydrogen bonds and elastic bonds, however, being impregnated so that it is possible at a following mechanical treatment of the product to divide the hydrogen bond into separate groups of fibers being connected with other groups through invisible minute lines containing elastic bonds. These invisible lines contain only elastic bonds. The mechanical treatment is preferably of the type which is described in copending patent application filed with the United States Patent Office under the title "Mechanical partly neutralization of hydrogen bonds for production of a softer and more silky air- laid fibrous product". According to the present invention a method is provided wherein a modification of the binder solution is effected by introducing a softener product into the binder suspension before its application onto the fibrous product. Introduction/modification of a softener product e.g. in the form of a SBR latex product into the fibrous product makes it possible to reduce the amount of binder and simultaneously it is possible to obtain a product which, after a following mechanical neutralization of the hydrogen bonds, is more soft and silky and stronger. Thus all the advantages obtained by the mechanical neutralization is also obtained in a product according to the present invention, however, surprisingly the product will occur even more soft and silky than normal and also stronger than normal. These advantages are described in the above-mentioned United States Patent Application. The surprising improvement in the qualities is difficult to explain. However, it is believed that the mechanical treatment of a latex bonded product will leave an elastic mosaicification between the fiber groups. Simultaneously, the paper product will be in a new quality. The hand and feel of the new product would be improved as compared to the hand and feel of a product with which the hydrogen bonds through the whole product are making stiffness, and the mechanical neutralization in very tiny lines are according to the invention subject to a mechanical neutralization process. It is to be noted that the hydrogen bonds due to their brittleness and fragility are normally not wanted in soft products used for hygienic purposes, diapers, wipers, etc. A hydrogen bond is irritating to the skin as a dry formed product consists of fibers arranged in groups in contact with or in connection with the other groups of fibers, then the product will result as a product being stronger than a product having only single fibers being in mutually contact or connection with other single fibers. Accordingly, a product having small groups of fibers being interconnected through the hydrogen bonds will not only be softer but also become stronger. This is due to the fact that the groups will be interconnected by latex bonds which are not interrupted with the mechanical method described below. Hydrogen bond is unavoidable because the latex solution is suspended in so much water that the hydrogen bond is all over and through the dry formed product. According to this invention the hydrogen bond will remain in very small areas or islands which have not been subjected to the neutralization stretching process. Thus the strongly coherence of the product will be maintained in said areas or islands and in the connected islands. The neutralization is effected by stretching the product at least in two directions, however, also a stretching in three or four directions is possible. Thereby flexibility lines are established in the bonds. Thus a more or less randomly orientated pattern is obtained in which the hydrogen bonds have been flexible in mini lines. However, due to the elasticity the latex bonds even after the stretched product, the product will all over have a latex bond. With this method an advantageous product is obtained having groups of interconnected fiber groups instead of single fibers. The final product will be soft in quality, be strong and have a good hand and feel and a good drapability. The effect of the neutralization of the hydrogen bonds in this mini line places is not visible even in a three dimensional microscope in the final products. They are almost microscopic, however, the quality of the final product has remarkable new qualities. Preferably the modified SBR latex is used after a whipping process. Hereby the latex product is mixed intimately into the solution thereby ensuring a good distribution of the product through the fibrous product. The mixing is done in the following way: According to a specific embodiment blown castor oil is added to the SBR latex binder. In such case the whipping process is advantageous, because it is an oxidation of the castor oil which hereby will be blown. The use of blown castor oil is advantageous in connection with a Styrene-Butadiene Rubber. It is preferred to add between 0.5% and 1 % by weight of the blown castor oil to the latex dry substance. It is essential that the blown castor oil is added slowly to the Styrene-Butadiene Rubber latex milk under an energetic whipping. Hereby, the advisably oxidation in the blown oil remains. According to a further possible embodiment the SBR latex product may be provided with milk which has given surprisingly good results. Thus, it is advantageous to use milk having a content of fat of between 8 to 15 % by weight, preferably having a content of fat of 10% by weight. Such milk will also comprise casein. The casein could occur in an amount of 2 to 3 % by weight in the milk. The casein will also provide good, however, brittle bonds. These brittle bonds may be compared with the hydrogen bonds and would make the product strong. As it is known, casein is insoluble in water. However, the casein bonds will be neutralized to the extent wanted together with the neutralization of the hydrogen bonds by the stretching of the product. It is believed that by stirring/whipping in an oxygen containing air, as normal air, or with little peroxide, the fat in the milk might be changed to a sort of blown oil. If a Styrene-Butadiene Rubber latex is used it is advantageous to add between 2 to 5 % by weight of natural latex in order to make the latex more elastic, and thereby making it possible to obtain a higher degree of stretching. When obtaining such higher degree of stretching a more fine pattern of invisible neutralization lines is obtained. It could be said that a mini-mosaic is obtained in which each of the mosaic sections contain small groups of fibers being interconnected by the hydrogen bonds and possibly also the casein bonds. Said sections being separated by a fine network of lines in which the hydrogen bonds and possible also the casein bonds, if any, are neutralized or released from their tension. Thereby a very strong and very soft product is obtained. The invention concerns also an apparatus for use in production of a soft and silky air laid fibrous product by dry-laying a fibrous product and comprising means for applying a binder solution onto the fibrous product in order to establish a combination of brittle bonds and elastic bonds, means for admixing a softener product into the binder solution before said solution is introduced into the application means. This apparatus makes it possible to add the softener product to the binder solution in the admixing means. The admixing means are preferably whipping means which make it possible to obtain an intimate mixing. Further features and advantages of the present invention will be understood by reference to the attached drawings taken in conjunction with the ensuing discussion. DESCRD7TION OF THE DRAWINGS In the drawings, Fig. 1-3 illustrate diagrammatically three embodiments of an apparatus according to the present invention, Fig. 4 an diagrammatically enlarged view of a fibrous product manufactured without the use of a method according to the present invention, Fig. 5 a view corresponding to the one shown in Fig. 4, however, having the fibrous product produced by use of a binder manufactured by a method according to the present invention, and Fig. 6 a schematically view for illustrating the mini-mosaic of the invisible flexibility line in the fibrous product illustrated in Fig. 5. Preferred embodiments for an apparatus according to the present invention is diagrammatically illustrated in Figs. 1-3. In these Figures identical or corresponding elements are designated with same reference numbers and will only be explained in details in connection with Fig. 1. The apparatus includes a fiber distributor 1, a suction box 2, and an endless foraminous forming wire 3 passing there between the endless forming wire consisting e.g. of a mesh net constructed using bronze wires. The forming wire 3 is driven by suitable means (not shown) so that it will continuously pass between the distributor 1 and the suction box 2. The forming wire 3 moves in direction of an arrow 4. The suction box 2 includes a suction pipe 5 which is connected to a fan (not shown) for the creation of a vacuum therein. The forming wire 3 passes through the nip of a pair of rollers 6,7 and below a nozzle 8 spraying a binder solution onto the product formed. The nozzle 8 is connected with a mixing box 10 according to the invention. The mixing box 10 is connected with supplying means 11 and 12. An endless band 13 is arranged in continuation of the forming wire 3. The band 13 is driven in direction of the arrow 14. A further endless band 15 is provided above the forming wire 3 and the endless band 13. The endless band 13 is a gas permeable band wounded on three rollers 16, 17, and 18. From the roller 17 a wall 19 is provided, thereby dividing the interior space of the gas permeable band 15 into two compart- ments 20 and 21. In the compartment 20 a vacuum is created through a fan (not shown), thereby lifting the fibrous product 22 free of the forming wire 3. In the compartment 21 an overpressure is created e.g. by means of the same fan which creates the vacuum in compartment 20. Thereby, the fibrous product 22 is transferred and deposited onto the endless band 13. The apparatus also comprises .two sets of rollers 23,24 and 25,26, respectively, and a further nozzle 8 which is mounted between said sets of rollers and to which a binder solution is supplied from the mixing box 10. The rollers 24 and 26 may preferably be heated rollers. Furthermore, the apparatus comprises a drying unit 27, a stretching unit 28, a curing unit 29, and a roller 30 for winding the final product. The stretching unit 28 shown in Fig. 1 comprises a series of four bombarded rollers 31. Between the bombarded rollers 31 turning and tightening rollers 32 are provided. The turning and tightening rollers 32 are movable along the arrows 33 in order to urge the fibrous product 22 against the bombarded rollers 31 with different forces, thereby effecting different degrees of stretching. The apparatus illustrated in Figs. 2 and 3 differs only from the apparatus illustrated in Fig. 1 by the use of other stretching units 28. The stretching unit in Fig. 2 comprises a single roller 34 having a surface provided with small protuberances thus providing a surface which corresponds to the surface known from a corncob, however, each protuberance is much smaller as compared to a corngrain. Furthermore, the stretching unit 28 comprises two turning and tightening rollers 35 being movable along arrows 36 in order to urge the fibrous product 22 against the roller 34 with different forces thereby effecting different degrees of stretching. The stretching unit 28 illustrated in Fig. 3 comprises a series of four rollers 37 and 38. The rollers 37 and 38 comprise a left hand thread and a right hand thread, respectively. The fibrous product 22 is led according to a sine-formed path through the series of rollers 37,38 alternately being urged into contact with a left hand thread and a right hand thread, thereby establishing a stretch as the fibrous product 22 is urged against the rollers 37,38 in a tightened manner. The threads provided on the rollers 37,38 are rounded, thereby allowing the fibrous product 22 to slide on the top of the threads. The apparatus shown in different Figures operates in the following manner: When the forming wire 3 is advanced in the above-mentioned path a fiber material is deposited on the forming wire 3 on which it is moved in direction of arrow 4 and forms a fiber layer when air is sucked away through the suction box 2. The fiber layer thus formed is rolled when passing the nip of the rollers 6,7. The binder material and the softener product is mixed in the mixing box 10. Then the binder solution 9 manufactured according to the invention is the applied to one side of the layer by means of the nozzle 8. The product thus formed has such a strength that it can be removed from the forming wire 3 by means of the gas permeable endless band 15. Due to the vacuum in the chamber 20 the fibrous product 22 is lifted free of the forming wire 3 and is then deposited onto the band 13 due to the oveφressure in the compartment 21. The fibrous product 22 is then passed through the set of rollers 23,24 and passes the nozzle 28 at which a binder solution 9 is applied on the side of the product facing downwards on the forming wire 3. When the material has passed the set of rollers 25,26 it is led through a drying unit 27. The rollers 24 and 26 are preferably heated so as to remove a part of the moisture supplied together with the binder solution. Thus is might be possible to obviate a use of a separate drying unit 27. After having passed through the drying unit 27 the fibrous product 22 is led through the stretching unit 28 in which the product is stretched at least in two directions. The effect on the stretching would be explained in more detail below. Before the product 22 is wound on the roller 30 it is led through a curing unit 29. If it is desired it is possible to provide a nozzle for adjusting the moisture content of the product before it is wound on the roller 40. The nozzles 8 are provided with a binder solution from a mixing box 10. The mixing box 10 comprises preferably mixing means in order to effect an intimate mixing by a whipping process. The product to be mixed in the mixing box 10 is provided from supply means 11 and 12. The supply means 12 contain a latex binder which preferably is a SBR latex binder in an aqueous suspension which is known in the art. It is noted that it is also possible to use other binders which are well-known in the art. The latex binder solution is modified by introducing a softener product from the supply means 11. The introduction of a softener product into the latex binder suspen¬ sion has given suφrisingly improvements in the qualities of the final product obtained in that it is more soft and silky and also stronger than normal after the stretching operation effecting in the stretching unit 28. According to a preferred embodiment the softener product is blown castor oil which is whipped into a SBR latex binder solution. The whipping process is advantageously because of the oxidation of the castor oil which thereby is blown. It is preferred to add between 0.5 % and 1 % by weight of the blown castor oil to a SBR latex dry substance. According to another preferred embodiment the softener product is milk having a content of fat between 8 to 15% by weight, preferably a content of fat of 10% by weight. Moreover, between 2 to 5 % of natural latex is added to SBR latex in order to obtain a more elastic latex, and thereby making it possible to obtain a higher degree of stretching. Such higher degree of stretching in the stretching unit 28 will provide a more fine pattern of mini-mosaic lines in which the hydrogen bonds are neutralized as explained above. The modification of the latex binder solution is essential in order to obtain the soft and silky product which is provided according to the present invention. The stretching unit 28 comprises bombarded rollers 31 which are well-known. However, so far bombarded rollers 21 have been used for smoothening a fibrous product. The fibrous product 22 is urged against the bombarded rollers 31 through the influence from the turning and tightening rollers 32, thereby applying the fibrous product 22 onto the rollers 31 with a force sufficient to effect a stretching. Preferably, each succeeding bombarded roller is driven with a higher surface velocity than a previous roller 31 in order to effect a stretching in the longitudinal direction of the product 22. Due to the stretching it is possible to obtain a fine pattern of invisible neu- tralization lines to be explained below. When using the corncob-shaped roller 34 illustrated in Fig. 2 it is possible to obtain a stretching around the smooth protuberances in the surface. The fibrous product 22 is also urged against the surface thereof by means of the turning and tightening rollers 35. Due to the great number of fine distributed and small protuberances a multi-di¬ rectional stretching is obtained due to the force with which the fibrous product 22 is urged against the surface of the roller 34. If desired the roller 34 may be followed by one or more bombarded rollers for effecting a smoothening. However, such smoothening process would not be necessary for the production of most products. The roller 34 might have protuberances having a height of between 2 mm and 3 mm and having a mutual distance between protuberances of between 5 mm and 20 mm. When using the thread-provided rollers 37,38 illustrated in Fig. 3 it is possible to stretch the product in order to obtain said mosaic of neutralization lines in the product 22. The thread is formed by a sine-shaped surface of the roller in which each sine- wave has a height of between 5 and 10 mm and having a mutual distance between the waves of between 10 and 15 mm. The roller may have a diameter of between 0.4 and 0.6 m. The same diameters could also be used for the rollers 31 and 34. In Fig. 4 a fragmentary enlarged view of a fibrous product 22 is illustrated. It is seen that the single fibers 39 are distributed with a normal air-forming distribution of the fibers 39 in all positions and with hydrogen bonds and latex bonds at cross-linking points of the individual fibers. Fig. 5 illustrates greatly enlarged a fibrous product 22 corresponding to that illustrated in Fig. 2, however, treated with a modified latex binder and subjected to a stretching process as described above. In the view a mosaic of lines 41 is illustrated separating the product in mosaic sections 42 in which the hydrogen bonds are maintained. In the lines 41 the brittle hydrogen bonds and casein bonds are neutralized whereas the elastic latex bonds are maintained even after the stretching of the product 22. The product will all over its surface maintain the latex bonds. Thus the product is obtained having groups of interconnected fibers 39 in the mosaic sections 42 when said groups of fibers are interconnected with other groups of fibers or single fibers through the latex bonds. Accordingly, a final product is obtained having a good hand and feel and a good drapability. In Fig. 6 the mosaic pattern of the lines 41 is illustrated without the illustration of the fibers 39. This is only for illustrative reasons as the lines 41 would be invisible in the final product even if it is studied through a three-dimensional microscope.

Claims: CLAIMS 1. A method for production of a binder solution which makes it possible to manufacture a soft and silky air-laid fibrous product having fibers and groups of fibers bonded to other fibers and other groups of fibers as the binder solution is applied to the fibrous product, characterized in that a softener product is admixed into the binder solution before its application onto the fibrous product. 2. A method according to claim 1, characterized in that the binder solution is a latex binder contained in a water suspension, and that the softener product is admixed into the water suspension by a whipping process. 3. A method according to claim 2, characterized in that the latex binder is based on a Styrene-Butadiene Rubber latex, and that 2 to 5% by weight of natural latex is added to the SBR latex milk. 4. A method according to claim 3, characterized in that 0.5 to 1 % by weight blown castor oil in relation to the SBR latex dry substance is added to the SBR latex milk. 5. A method according to claim 4, characterized in that the blown castor oil is added slowly to the SBR latex milk, and that a simultaneous whipping of the binder solution is effected. 6. A method according to claim 1, characterized in that the fatty product is milk having a content of fat of between 8 to 15 % by weight, preferably between 9 and 11% by weight. 7. A method according to claim 6, characterized in that the milk is added with a simultaneous whipping of the solution in an oxygen containing air. 8. A method according to claim 6, characterized in that the milk is added together with a little peroxide under a simultaneous whipping of the binder solution. 9. An apparatus for use in production of a soft and silky air laid fibrous product by dry-laying a fibrous product characterized in that said apparatus comprises means for applying a binder solution onto the fibrous product in order to establish a combination of brittle bonds and elastic bonds, means for admixing a softener product into the binder solution before said solution is introduced into the application means. 10. An apparatus according to claim 10, characterized in that said admixing means comprise whipping means for whipping the greasy product into the binder so¬ lution.

Inventors: KROEYER KARL KRISTIAN KOBS, KROEYER, KARL, KRISTIAN, KOBS
Applicants: KROYER K K K, KROEYER, KARL, KRISTIAN, KOBS
Application year: 1994
Main classification: D21H17
IPC codes: D04H1